A form of an information storage and retrieval device is a hard disk drive (hereinafter “disk drive”). A disk drive is conventionally used for information storage and retrieval with computers, data recorders, redundant arrays of independent disks (RAIDs), multi-media recorders, and the like. A disk drive comprises one or more disk media.
Each disk medium comprises a substrate upon which materials are deposited to provide a magnetically sensitive surface. In forming a disk medium, a substrate is ground or polished, conventionally by chemical-mechanical or mechanical polishing, to provide a substantially planar surface. Layers of materials are substantially uniformly deposited on this substantially planar surface to provide magnetic properties for writing to and reading from the disk media.
However, surface irregularities, waviness may affect the surface topography of the disk medium, and need to be detected and characterized. A number of different types of apparatus can be used to measure the surface topography. These include a quadrature phase shift interferometer, or a laser doppler vibrometer, for example. However, dynamic measurements of hard disk static surface topography provided by these instruments, such as the measurement of HMS_Wq (r.m.s. Head-Media Spacing Modulation) are easily contaminated by additional out-of-plane motion from disk flutter associated with disk resonance modes.
Disk modes are characterized by their specific temporal frequencies and their specific spatial patterns. The frequencies of the disk modes are determined by the material mechanical properties, such as stiffness and mass density, and disk geometry. By contrast, the spatial wavelengths of the disk modes are determined solely by the disk geometry. The disk modes can be excited by windage, mass imbalance, spindle motor vibrations, or a combination of these factors.
Time-domain disk surface out-of-plane motion associated with the disk modes is also detected, along with the static disk surface topography, using time-domain measurement techniques such as quadrature phase shift interferometry and laser doppler vibrometery. Because there is a total disconnect between the temporal and spatial frequencies associated with each disk mode, this out-of-plane motion captured by the time-domain techniques can significantly distort the space-domain disk surface topography obtained from time-domain measurement. As a result, the accuracy of calculated HMS_Wq results can be severely degraded.